The three injured youths -- Jhonata Cruz Ventura (15 years), Cauan Emanuel Gomes Nunes (14), and Francisco Diogo Bento Alves (15) were taken to area hospitals, the club said on Friday. Ventura remains in critical situation with burns on 30 percent of his body.

13 other players escaped the sleeping quarters.

"We are distraught," Flamengo president Rodolfo Landim said outside the complex, where friends, fans and neighbors gathered, some forming a circle to pray. "This is the worst tragedy to happen to the club in its 123 years."

Landim did not take questions from reporters who were also outside the complex and gave no details about the players involved, but added: "The most important thing right now is to minimize the suffering of these families."

Rio fire service lieutenant Colonel Douglas Henaut told reporters: "We managed to rescue the victims that were outside ... The place was completely overtaken by fire. As much as we tried to get inside and find people still alive, that wasn't [possible]. ... We only found bodies inside.

"We can't tell you the cause of the fire; that needs to be investigated."

Flamengo is one of the best-supported clubs in Brazil and known around the world. Known by fans as the Red-and-Black, the club won the Copa Libertadores, South America's version of the Champions League, in 1981 and lifted the Intercontinental Cup a few months later.

Aerial imagery filmed by RecordTV and O Globo broadcasters shows a red-black area destroyed by flames. The fire was reportedly controlled around 7:20 a.m.

One young player told reporters the fire started in his room.

"The air conditioner caught fire, and I ran out," said Felipe Cardoso, a midfielder with the under-17 side. "Thank God I managed to run and I'm still alive."

The Rio de Janeiro mayor's office said that the dormitory destroyed by the blaze was built on land that was not registered for buildings and that the club had no permission to erect lodgings there.

"On the project protocol the area is described as a parking lot," the office said in a statement. "There is no register of a new request for a license to use the area as a dormitory."

This is the second tragedy to hit Rio de Janeiro in the past 48 hours after at least six people died following a storm that caused floods and mudslides on Wednesday night.

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Deadly fire at Flamengo's Rio training centre

A fire on Friday left 10 people dead and three people injured at Flamengo's training centre in Rio de Janeiro.

Rio de Janeiro's governor, Wilson Witzel, has declared three days of mourning for the deaths of those affected by the floods and the fire, and President Jair Bolsonaro issued a statement lamenting that the fire had taken "the young lives at the beginning of pursuing their professional dreams."

Real Madrid forward Vinicius Junior, who trained at the centre while being a part of Flamengo's youth academy before moving to Spain, tweeted: "What sad news! Let's pray for everyone. Strength, strength and strength."

He added: "Just to remember the nights and days that I spent [at the centre], is to shiver. Still not believing, but in prayer for all! May God bless each one's family!"

Club legend Zico wrote on Instagram: "May God comfort the families who lost their children, grandchildren, brothers, nephews, relatives. Youngsters that dreamed of having a future in their lives and many, without a doubt, looking to help their families ... Lives are gone. May the Black and red nation have the strength and faith to overcome this moment."

Ronaldinho, another product from their club's academy, said on Twitter: "It is a very big sadness, my thoughts and condolenses are with all the family members and the Red-and-Black nation. Terrible tragedy!!!"

Pele provided his sentiments, saying: "My day started with the news of about the [training camp] of @Flamengo -- a place where young ones pursue their dreams. It is a sad day for Brazilian football."

Officials postponed Saturday's two semifinals of the Guanabara Cup, one of which was between Flamengo and Rio rival Fluminense.

Brazilian clubs commonly host young players in dormitories while they are training with youth teams or at the club for trials, especially those from poor backgrounds or from outside the city.

However, many of the lodgings have a reputation for poor health and hygiene standards. In recent years, major clubs such as Vasco da Gama, Botafogo and Parana have hit the headlines due to the precarious conditions of their training centres.

After years of financial difficulties, Flamengo last year spent 23 million reais ($6.2 million) to expand the Ninho do Urubu training ground, which was being used both by the first team and youth squads.

In addition to accommodation for young players, the facilities include several pitches, an aquatic park, a gym, a medical centre and a mini-stadium.

Information from Reuters and the Associated Press were used in this report.